A composite model of leptons and quarks

A heuristic model is presented, treating leptons and quarks as composites of spin $\text{1}\text{2}$ fields with charges 0, $\text{±}\text{e}\text{3}$. A distinguishability assumption leads to the emergence of three quark colors. The model is extended to consideration of the force-mediating bosons.     

Towards a realistic composite model of quarks and leptons

Within the context of the 't Hooft anomaly matching scheme, some guiding principles for model building are discussed with an eye to low-energy phenomenology. It is argued that Λ_ch (chiral symmetry breaking scale of the global color-flavor group G_CF) ≈ Λ_MC (metacolor scale) and Λ_gCF (unification scale of the gauge subgroup of G_CF) ≲ Λ_ch. As illustrations of the method, two composite models are suggested that can give rise to three or four generations of ordinary quarks and leptons without exotic fermions.     

Flavour changing neutral processes in a composite model for quarks,leptons and technifermions

It is argued that flavour-changing neutral processes may be suppressed in a recently proposed composite model for quarks, leptons and technifermions, in which the technicolour dynamics are asymptotically non-free at the composite level and are assumed to have an ultraviolet fixed point.     

Generations of massless composite quarks and leptons

We present a QCD-like composite model in which quarks, leptons and technifermions are three-body systems made out of three kinds of massless elementary fermions t, c and w, each carrying technicolor, color and weak gauge interactions, respectively. Discrete symmetries, remnants of the U(1)_A of the original lagrangian, are responsible for the masslessness of all the quarks and leptons and give the precise meaning of the generations. The model exhibits three generations for both quarks and leptons. Small but non-zero masses of the quarks and leptons are produced by the technicolor condensate of the composite technifermions, which thereby leads to the non-trivial Cabibbo mixing. Proton decays are all forbidden at the mass scale of the QCD-like theory.     

Four families of composite quarks and leptons

Four families of composite quarks and leptons, two standard and two non-standard, are found in a unique solution SU(3)_HC × SU(6)_L × SU(6)_R of a restricted 't Hooft anomaly-matching program. Testable predictions emerge, such as prohibition of μ → eγ, zero charge asymmetry in e⁺e^? → τ⁺τ^? in contrast to e⁺e^? → μ⁺μ^?, and a rich new hadron spectrum masses around M_W. A minimal set of spectator fermions contains color-singlet objects with fractional quark-like charges.     

QDD—a model of quarks and leptons

An economical scheme for composite quarks and leptons is suggested. The basic vector particles of the theory are, like gluons, confined and the intermediate vector bosons are also composites. A possible “reason” for the existence of families emerges.     

Constraints on composite models of quarks and leptons

The previously noted difficulty of obtaining Dirac magnetic moments in composite models is combined with the observation that a “light” bound fermion state with a small size must have the Dirac moment in a renormalizable theory since its anomalous moment is determined by its excitation spectrum. New constraints on composite models are given, including the decoupling of low-lying excitations and the “superconfinement” condition that creation of virtual electron-positron pairs by the superstrong gluons responsible for binding the constituents of the electron must be strictly forbidden in photon-electron scattering.     

The magnetic moment of composite leptons and quarks

We show that for a composite fermion of sufficiently small radius, the magnetic moment approaches the Dirac value corresponding to the overall charge and mass, regardless of the constituent values. This resolves a recently suggested difficulty in composite models of leptons and quarks.     

The structure of weak interactions for composite quarks and leptons

We consider a model of quarks and leptons as quasi-Goldstone fermions which is based on an underlying supersymmetric SU(2)_HC × SU(2)′_HC preon theory. The spontaneous breakdown of a global U(6) × U(6)′ × U(1) symmetry to U(4) × U(4)′ × SU(2)_diag creates both quarks and leptons and at the same time allows for the possibility of having either residual or fundamental weak interactions. Effective lagrangians in the confining phase of the theory are compared to those emerging from a complementary picture and the problems connected with the nature of the weak interactions are discussed in this context also.     

Composite model of quarks and leptons related to composite structures of SO(10)

It is demonstrated that the composite structure of quarks and leptons can be embedded in the SO(10) model of the strong and electroweak interactions. There appear two entities: two bosonic spinors ξ and ξ′ of SO(4) and a fermionic spinor B of SO(6). All the $\text{16's}$ of fermions can be expressed as (ξjB_α) and $\text{(ξ′j}\text{B}{}^1{}_{\mathrm{\alpha }}\text{)}$, where j=1 or 2 and α=0, 1, 2, 3 indicating the color SU(4) indices. Further consideration leads us to find a basic entity, ζ transforming as 5 under SU(5), of which the charge is $\text{(+}\text{1}\text{2}\text{, 0, ?}\text{1}\text{6}\text{, ?}\text{1}\text{6}\text{) ?}\text{1}\text{6}\text{)}$ and ξ,ξ′ and B can be constructed from ζ and $\text{ζ}$. Although ξ,ξ′ and B obey the SO(10) gauge group, ζ cannot be controlled by SO(10). Some unknown interactions may govern the behavior of ζ at very high energies, where the unification based on SO(10) with ξ,ξ′ and B is destroyed.     

Fourth generation of quarks and leptons

Permutation Symmetry sugests an intergeneration quark-lepton mass formulam _μ /m _τ /m _L =m _s /m _b /m _b′ =m _c /m _t /m _t′ . We consider several possibilities We consider several possibilities for the fourth generation masses.     

Signals of excited quarks and leptons

e⁺e^? annihilation to two photons (including beam polarization) and quark-antiquark annihilation to gluons are discussed as possible tools to investigate the existence (and handedness) of excited electrons and quarks. Properties of these particles can also be explored in eγ and ep colliders; production cross sections and the impact of these particles on structure functions are derived.     

Constituent models for quarks and leptons

Constituent models predicting several families of quarks and leptons are presented. They satisfy 't Hooft's anomaly conditions and a “principle of exclusion” introduced here. Some mechanisms for breaking GSW symmetry and generating masses for quarks and leptons consistent with the GIM mechanism are also given.     

On the excited quarks and leptons

Using a duality-like finite energy sum rule, we discuss the assumption of having excited fermions at the W scale in a supersymmetric(SUSY) and non-supersymmetric hypercolour theory where quarks and leptons are bound states of fermion and scalar preon constituents. We conclude that a SUSY-like composite model cannot have excited fermions having a mass smaller than 0.5 TeV. A non-SUSY composite model having composite fermions but elementary W bosons can produce an excited fermion mass of the order of M_W provided that the scalar vacuum condensate is of the order of the (TeV)² scale of compositeness.     

Composite quarks and leptons and horizontal symmetries

We describe models of composite quarks and leptons in which an explicit generation quantum number is carried by one of the preons. We find several possible solutions for the subcolor and the horizontal groups.     

Seesaw mass matrix model of quarks and leptons with flavor-triplet Higgs scalars

In a seesaw mass matrix model with a universal structure of , as the origin of m_L (m_R) for quarks and leptons, flavor-triplet Higgs scalars whose vacuum expectation values v_i are proportional to the square roots of the charged lepton masses m_ei, i.e. , are assumed. Then, it is investigated whether such a model can explain the observed neutrino masses and mixings (and also quark masses and mixings) or not.     

Mass spectral condition for leptons and quarks

Consideration is given to the mass spectral conditiona(a,_m)a =a _m, wherea is the annihilation operator forQ=–1 states in the Hilbert space of leptons and quarks anda _m is the commutator resolvent ofa with respect tom. It is observed that this spectral condition, which simply requires a to be a congruent automorph ofa _m , implies that the third-, fourth-, and fifth-generationQ=-1 leptons have the masses 1788.03 MeV, 42.1649 GeV, and 1.33422 TeV, respectively. With the assumption that the mass spectral condition also holds forQ=0 states in the Hilbert space, one obtains new theoretical upper and lower bounds on the neutrino masses.